I have a 1970 Mercury 650 65 horse 4cylinder on a 1970 15' Las Vegas tri hull. I bought the boat about a month ago and love it. I got it to use mainly for trolling. The motor starts and runs well at idle and full throttle. I put it in forward and let it run in idle to troll. I have taken it out twice so far and the first time I almost ran out of gas by noon with about 5 gallons of gas in the tank. Thats about a gallon an hour idling. When I got home I turned the idle mixture screws in about a 1/4 turn to see if it was just running too rich. I took the boat out yesterday and it didn't want to start as easily or run in gear at idle so I returned the idle screws to about the original position. My understanding is that it should be using approximately .3 gallons per hour which seems way more reasonable. Any opinions at all would be greatly appreciated.